The present invention relates to a method for producing a tubular needle punched felt, and more particularly to a method for producing a seamless tubular needle punched felt which can be suitably used as a needle punched felt for Insituform method (hereinafter referred to as "INS method"), and the like.
In these days, INS method has been developed as a technical method for repairing a pipe and the like buried under the ground, and attracts public attention.
The INS method is a very useful technique for repairing a pipe which is buried under the ground since the pipe can be completely repaired without digging up the pipe. The INS method comprises the steps of:
(a) using a tubular felt which is impregnated with a thermosetting resin, which is not yet cured, and of which outside surface is laminated with a film, PA0 (b) fixing one edge of the reversed tubular felt with an inlet port of a pipe to be repaired, PA0 (c) inserting the tubular felt into the pipe with accelerating the reversing of the tubular felt by pressing the outside surface of the tubular felt in the pipe with water, and PA0 (d) curing the thermosetting resin impregnated in the tubular felt by heating the water in the pipe by means of a boiler and the like. PA0 (a) rolling a long web having a sheet form to give a tubular web, PA0 (b) contacting both edges facing each other of the web so that the both edges form a butt-joint, PA0 (c) stitching both edges so that a thread crosses the both edges, and PA0 (d) laminating a ribbon for sealing on the stitched surface or coating the stitched surface with a resin to give a tubular felt. PA0 (a) the obtained tubular needle punched felt does not generate foams and cracks on the surface of the felt at the time of curing the resin impregnated in the felt since the needle punched felt is seamless and is uniformly impregnated with a resin, PA0 (b) the method achieves the improvement of efficiency, labor saving and excellent profitability and removes conventional complexities entirely as well as it becomes easy to produce the product by means of this method since this method is free from working for seaming and sealing of the stitched surfaces in the producing steps, PA0 (c) the method is free from changing the equipments owing to sizes of diameter of the desired tubular needle punched felt since the tubular needle punched felt having a desired size of the diameter can be obtained only by changing the size of the sheet, and PA0 (d) efficiency of producing the tubular needle punched felt can be extremely improved since continuous production can be conducted in accordance with this method. PA0 (a) overlapping not less than two long sheets comprising a web to form thin layer portions at both side edges of the overlapped sheets and a thick layer portion at the central portion of the overlapped sheets by dislocating the sheets in width direction; PA0 (b) needle punching one part or whole of the above central thick layer portion of the overlapped sheets to form a lapped sheet; PA0 (c) rolling the lapped sheet and transforming the lapped sheet into a tubular one and overlapping the above thin layer portions with each other; and PA0 (d) needle punching the above overlapped thin layer portions to make the thin layer portions one body.
Conventionally, the technics described in Japanese Examined Patent Publication No. 33098/1983 has been employed for producing the tubular felt which is used in the INS method.
The method for producing a tubular felt described in Japanese Examined Patent Publication No. 33098/1983 is a method characterized in that:
However, the above method for producing a tubular felt has the following problems with regard to the product and producing steps.
When a thermosetting resin is impregnated into the obtained tubular felt, the butt-joint of the tubular felt is scarcely impregnated with the resin, so that foams are likely to generate in the butt-joint. Therefore, cracks are easy to generate on the surface of the resulting final product.
The above method has a very low productive efficiency since special seaming works are required in the producing steps and there are necessitated many complicated steps in the above method.
Further, the obtained tubular felt is easy to generate strain and gaps particularly at the butt-joint being outside of the tubular felt since there is a difference between the length of the inside circumference and that of the outside circumference of the tubular felt as the result of rolling the sheet having a certain thickness.
The object of the present invention is to solve the above-mentioned problems of the conventional tubular felts and to provide a method for producing a tubular needle punched felt which exhibits following preferable effects:
These and other objects of the present invention will become apparent from the description hereinafter.